Epigenetic regulation is a fundamental mechanism that bridges the genome with the environment, and is emerging as a key determinant of longevity. Recent findings in C. elegans have provided strong evidence that epigenetic mechanisms, in particular chromatin regulation, are intimately involved in longevity determination and its inheritance. Despite the exciting biological data, the mechanisms of how epigenetic regulation influences longevity are unclear. The long-term goal of this application is to elucidate how epigenetic regulation bridges the genome and the environment to modulate longevity. The overarching hypothesis of this proposal is that we can gain mechanistic insights into the connection of epigenetic regulation and longevity by studying longevity mutants with disrupted epigenetic mechanisms and by probing how the overall epigenetic landscape changes with age in the powerful model C. elegans. Building on recent discoveries in my lab, we will pursue three specific aims. In Aim 1, we will investigate the mechanisms by which the putative H3K9me3 methyltransferases SET-9 & SET-26 limit lifespan and maintain germline immortality. We propose to determine the longevity pathways they act in, identify the protein domains and the tissue specificity key to their action, and map their genome-wide binding profiles and transcriptional outputs. The proposed investigations will reveal how SET-9/26 influence longevity and transgenerational inheritance. In Aim 2, we will investigate the role of H3K36me3 in age-dependent gene regulation and longevity. We propose to examine whether altered RNA polymerase II-mediated transcription contributes to age-dependent gene expression changes, identify the factors that recognize the H3K36me3 mark, and monitor the biological consequence of depleting H3K36 methylation in specific cells/tissues. H3K36me3 is a ubiquitous histone modification, thus elucidating its mechanism in gene expression regulation through the aging process will provide important new insights into not only aging biology but also fundamental mechanisms of gene regulation. In Aim 3, we will investigate how the chromatin landscape changes with age. Currently not much is known about how aging impacts the general chromatin landscape in C. elegans. We propose to profile the genome-wide patterns of several key histone modifications, as well as nucleosome density, through the aging process, and use computational methods to uncover age-dependent patterns that can generate testable hypotheses for future studies. Findings from our proposed investigations will provide a much-needed framework for integrating emerging functional data to understand how the epigenome modulates aging and longevity in C. elegans. The data generated in this aim will also be a useful resource for the aging and gene regulation research community. The proposed research will provide substantial new insights into how epigenetic mechanisms influence aging and longevity in the key model organism C. elegans, and will more broadly impact the understanding of the epigenetic basis of longevity in diverse organisms.